BRPI0518400B1 - METHOD OF PRODUCTION OF A HYDROGEN STORAGE MATERIAL, MAGNESI-NICKEL ALLOY STORAGE AND HYDROGEN STORAGE MATERIAL FORMED FROM A Fused MAGNESIUM NICKEL ALLOY - Google Patents

Abstract

A method of producing a hydrogen storage material including the steps of: forming a magnesium-nickel melt having up to 50 wt % nickel; adding up to 2 wt % of a refining element to the melt under a non-oxidizing atmosphere, the refining element having an atomic radius within the range of 1-1.65 times the atomic radius of magnesium, such as at least one element selected from the group consisting of Zr, Na, K, Ba, Ca, Sr, La, Y, Yb, Rb and Cs; and solidifying the melt to produce the hydrogen storage material.

Description

(54) Title: PRODUCTION METHOD OF A HYDROGEN STORAGE MATERIAL, MAGNESIUM-NICKEL HYPHOEUTHETICAL ALLOY AND HYDROGEN STORAGE MATERIAL FORMED FROM A MAGNESIUM-NICKEL LAG. 00; C22C 1/02 (30) Unionist Priority: 07/12/2004 AU 2004907006 (73) Holder (s): HYDREXIA PTY LIMITED (72) Inventor (s): ARNE KRISTIAN DAHLE; KAZUHIRO NOGITA

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METHOD OF PRODUCTION OF A HYDROGEN STORAGE MATERIAL, MAGNESIUM-NICKEL HYPOEUTHETIC ALLOY AND HYDROGEN STORAGE MATERIAL FORMED FROM A ALLOY

Fused MAGNESIUM-NICKEL

FIELD OF THE INVENTION [001] This invention relates to hydrogen storage materials and specifically refers to a molten alloy that can be used as a hydrogen storage material.

BACKGROUND OF THE INVENTION [002] As the world population expands and economic activity increases, there are ever increasing signs that increasing atmospheric concentrations of carbon dioxide are warming the earth causing climate change. While the eventual depletion of oil and fossil fuel energy sources in the world will inevitably need to discover other economic sources of energy, the most obvious signs of global warming have increased the pressure for global energy systems to abandon carbon-rich fuels, whose combustion produces carbon monoxide and carbon dioxide gases.

[003] Hydrogen energy is attracting a lot of interest and is expected to eventually be a replacement for petroleum-based fuels. However, there are still several technical issues and barriers that must be overcome before hydrogen can be adopted as a practical fuel, the main obstacle being the development of a viable hydrogen storage system. Although hydrogen can be

2/14 stored as a compressed gas or liquid, the former occupies a large volume and the latter requires intense energy for production, reducing any environmental benefit. In addition, both hydrogen gas and liquid are potentially dangerous if the pressure storage containers are ruptured.

[004] A more compact and safer method of storing hydrogen is within solid materials. When infiltrated with hydrogen at relatively low pressures, metals and intermetallic compounds can absorb large amounts of hydrogen in a solid and safe manner. The stored hydrogen can be released when needed, simply by heating the alloy. The storage of hydrogen as a solid hydride can provide a weight percentage storage greater than that of compressed gas. However, a desirable hydrogen storage material must have a high storage capacity with respect to the weight of the material, an appropriate desorption temperature, good kinetics, good reversibility and be relatively low cost.

[005] Pure magnesium has a theoretical theoretical hydrogen transport capacity of 7.6% by weight. However, the resulting hydride is very stable and the temperature must be increased to 278 ° C for the hydrogen to be released. This desorption temperature makes such materials economically unattractive. A lower desorption temperature is desirable not only to reduce the amount of energy needed to release hydrogen, but to allow efficient use of vehicle exhaust heat to release hydrogen. Compared to magnesium

3/14 pure, the Mg ₂ Ni compound has a hydrogen storage capacity of 3.6% by weight, but importantly, the temperature required for hydrogen release is increased to less than that of pure magnesium. The hydrogen storage mechanism is believed to involve the formation of (solid) hydride particles, that is, MgH ₂ and Mg ₂ NiH4 in the microstructure.

[006] Recently, thixotropic casting techniques followed by partial reflux and saturation were used [YJKim, TWHong: Materials Transactions 43 (200) 17411747] to produce hypoeutectic Mg-Ni alloys consisting of magnesium-rich dendrites surrounded by Mg-Mg ₂ Refined eutectic Ni. These alloys absorb large amounts of hydrogen, similar to pure magnesium and reveal only a simple hydrogen absorption plateau in the pressure-composition-temperature curve (PCT), that is, non-separable plateaus for each phase. It is believed that nickel and / or the Mg ₂ Ni phase act as a catalyst, improving the hydrogen transfer kinetics in the magnesium-rich solid phases through the formation of MgH ₂ .

[007] This achievement has encouraged research [see review by S. Orimo and H. Fuji, Applied Physics A 72 (2001) 167-186] using nanotechnology and powder metallurgy techniques to produce materials with large internal interfacial areas . These techniques are attractive because they result in large areas of interface and introduce crystallographic defects, such as displacements and twinning, that would distribute potential catalysts through the microstructure, allowing them to have a widespread influence on the reaction kinetics. Unfortunately,

4/14 nanoscale powder metallurgy techniques offer limited control over the crystallographic structure of the phases (ie interfaces, twinning, etc.). The powder would be highly explosive and would be prohibitively expensive for mass and large-scale production of commercial hydrogen storage components. No research reported to date considers methods by which the high development of hydrogen storage components can be produced using processes that are cheaper and more applicable to mass production.

[008] It is an objective of the present invention to provide an alloy

of MgNi mergable with capacity of storage in hydrogen improved. [009] Reference to any technique previous at the report descriptive no is, nor should it be taken as one knowledge or any form of suggestion that that previous technique is part of the knowledge common general at

Australia or any other jurisdiction.

SUMMARY OF THE INVENTION [010] According to one aspect, the invention can provide a method of producing a hydrogen storage material including the steps of magnesium-nickel melting having additions of at least one refinement element, the element of refinement being able to promote a refined eutectic structure with increased twinning in the magnesium-nickel intermetallic phase and solidification of the magnesium-nickel fusion in a hydrogen storage material with said refined eutectic structure.

[011] In a preferred embodiment, the magnesium fusion5 / 14 nickel is formed by the steps of adding nickel to the magnesium fusion to produce a hypoeutectic magnesium-nickel alloy (ie greater than zero - 23.5% by weight) (Ni), homogenization of the magnesium-nickel fusion and addition of the refining element or elements to the melting under a protective atmosphere at addition ratios greater than zero and up to 2% by weight and preferably greater than zero and less than 500 ppm.

[012] The refinement element has an atomic radius within the range of about 1-1.65 times that of magnesium. It is understood that the refinement elements with atomic rays within this range will provide the refined eutectic structure discussed above. The refinement elements are selected from the group comprising Zr, Na, K, Ba, Ca, Sr, La, Y, Yb, Rb, Cs and rare earth elements, such as I. Zirconium is added to granulate the refining of crystals of magnesium and when used requires at least one more of the elements of the group.

[013] In another aspect, the invention can provide a method for producing a hydrogen storage material comprising the steps of forming hypoeutectic magnesium nickel fusion having additions of at least one refinement element having an atomic radius within the range of 1- 1.65 times that of magnesium, the refinement element being provided in the melt at addition rates greater than zero and up to 2% by weight and preferably less than 2,400 and more preferably less than 500 ppm and melting of the magnesium-nickel melt.

[014] The solidification stage in both aspects is a casting stage, where the metal is melted by a

6/14 appropriate procedure, such as spilling into preheated metal molds that cool the spill. The solidification step can be another controlled solidification process. However, once the alloy has melted, it is then subjected to activation and use as a hydrogen storage material. The alloy is preferably used in the casting condition.

[015] In another embodiment of the invention, a hydrogen storage alloy is provided comprising or consisting essentially of hypoeutectic magnesium-nickel alloy having more than zero and up to 2% by weight of a refinement element, the refinement element having a atomic radius of about 1-1.65 times that of magnesium; and the rest of magnesium and incidental impurities.

[016] Refinement additions are selected from the group of Zr, Na, K, Ba, Ca, Sr, La, Y, Yb, Rb, Cs and rare earth elements with addition rates above zero and up to 2% in weight and preferably greater than zero and less than 2,400 or more preferably greater than zero and less than 500 ppm. The most preferred addition elements are sodium and zirconium.

[017] Depositors have found that, by adding trace elements having atomic rays around magnesium up to 1.65 times the atomic rays of magnesium in relation to hypoeutectic MgNi systems, twinned crystal defects are promoted in the intermetallic phase of MgzNi. Increased refinement and crystal defects in the Mg2Ni phase are believed to catalyze the hydration reaction in the magnesium-rich solid phases of the alloy, thereby increasing the alloy's ability to absorb hydrogen and the kinetics of

7/14 hydrogen absorption.

[018] Additionally as the material is produced by a melting solidification process, it is a more commercially viable process for large-scale production of hydrogen storage components.

Description of the Drawings and Preferred Embodiment [019] Objectives and additional advantages of the present invention will be clear from the following description of the preferred modality and attached drawings where:

Figure 1 is a graph of pressure, composition, temperature of an unmodified magnesium alloy with 14% Ni,

Figure 2 is a graph summarizing the activation time at 350 ° C with 2 MPa for Examples 1-6,

Figure 3 is a graph of the PCT absorption data at 350 ° C and 2 MPa for Examples 1-6,

Figure 4 is a graph of the PCT absorption data at 300 ° C and 2 MPa for Examples 1-6,

Figure 5 is a graph of the PCT absorption data at 250 ° C and 2 MPa for Examples 1-6,

Figure 6 is a graph summarizing the absorption capacity of PCT at 350 ° C and 2 MPa,

Figure 7 is a graph illustrating the relationship between absorption and desorption for unmodified Mg 14 Ni alloy,

Figure 8 is a graph of 0.2 MPa desorption data for Examples 1-6, and

Figures 9 (a) -9 (h) are SEM micrographs of the cast alloys of Examples 1-6.

[020] The hydrogen storage material is produced according to the invention by forming a

8/14 hypoeutectic magnesium-nickel by adding nickel to molten magnesium. The addition of nickel can be up to 20% by weight and preferably 10-20% by weight of nickel. The melt is then mixed to provide a homogenized mixture.

[021] To this magnesium-nickel alloy, trace elements of crystallographic modification material are added. The added elements are those that refine the magnesium phase and promote a refined eutectic structure with increased twinning in the magnesium-nickel intermetallic phase.

[022] The range of elements that satisfy the two criteria above has atomic radii around that of magnesium and up to 1.65 times that of magnesium and include Zr, K, Na, Ba, Ca, Sr, La, Y, Yb, Rb, Cs and rare earth elements. The preferred elements used are sodium and / or zirconium.

[023] The fusion is again stirred to homogenize the mixture and keep under a protective atmosphere during the homogenization step. The protective atmosphere is any atmosphere that prevents magnesium from burning. Typical atmospheres include SFê and HFC-134a.

[024] The metal is then melted by an appropriate melting procedure, such as pouring into preheated metal molds.

[025] Although not wishing to be restricted to a specific theory of operation, it is considered that the increase in crystal defects, interfacial areas and displacement density catalyzes the hydration reaction in the magnesium-rich solid phases of the alloy, thus increasing the capacity and alloy kinetics for hydrogen absorption.

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Examples [026] The hydrogen absorption of the metal hydride alloy is characterized by the use of pressure, composition, temperature equilibrium (PCT) data. These data are obtained by maintaining a sample of alloy at constant temperature, while precisely measuring the amount of hydrogen absorbed and the pressure at which sorption occurs. The amount of hydrogen absorbed is expressed in terms of alloy composition, either as an atomic ratio of hydrogen atoms to the number of atoms in the base metal alloy or as the capacity of hydrogen in the material is a weight percentage basis .

[027] PCT stands for pressure-composition-isotherm and shows the maximum possible hydrogen absorption capacity at a fixed temperature. At pressure absorption is higher than that in desorption and the plateau region indicates the appropriate range for practical storage / release applications.

[028] Most of the hydrogen is absorbed in a range where there is little change in pressure. This region of constant constant pressure is known as the pressure plateau. The formation of metal hydride is also accompanied by hysteresis, which appears as the difference between the upper absorption curve and the lower desorption curve.

Example 1 [02 9] An unmodified magnesium alloy containing 14% by weight of Ni was subjected to a hydrogen atmosphere of 2 MPa at 350 ^and C for a period of 20 hours. The temperature, composition, pressure data were recorded and shown in figure 1.

10/14 [030] From figure 1, the activation time (At) of the alloy can be determined. The Activation Time indicates how fast an alloy becomes ready for use as a hydrogen-absorbing alloy. Shorter activation times save energy and are indicative of fundamental material differences in the kinetic performance of the alloys. Note that activation is generally required only once in the life cycle of a hydrogen storage alloy. Once the alloy is activated, the hydrogen absorption time is significantly reduced as evidenced by the last operating cycles.

Examples 2-6 [031] The magnesium nickel alloy of Example 1 was modified by the addition of a refinement element.

[032] Table 1 shows the element of refinement and the rate of addition of that element.

Table 1

Example Refinement Element Addition rate 2 At 2,400 ppm 3 At 600 ppm 4 Here 800 ppm 5 I 600 ppm 6 Zr 2% by weight

[033] The activation time of these examples is summarized in figure 2. From these results, it can be seen that the activation time can be reduced by about 40% compared to that of the unmodified alloy (from 8 hours to 3, 8 hours) . Consequently, for alloys at least up to the addition rates, the activation time can be significantly reduced. This has practical significance, but in a way

11/14 more importantly, it is indicative of the superior kinetic performance of the modified alloy.

[034] The graph shown in figure 3 was produced, when the data collected in the examples above were analyzed with reference only to the absorption curve.

[035] PCT curves (absorption only) at 350 ° C show that all six samples can absorb about 7% by weight of hydrogen. There is a small difference between the samples. 100% pure Mg absorbs 7.6% by weight of hydrogen and 7% by weight of hydrogen absorption is close to the theoretical limits for a sample of Mg with 14% by weight of Ni. The primary phases of Mg are considered to be the hydrogen absorption phases and eutectic regions are considered to have a catalytic function improving the hydrogen kinetics.

[036] The alloys of Examples 1-6 were then characterized at 300 ° C and 250 ° C with the absorption results shown in figures 4 and 5 respectively.

[037] At lower temperatures, there is a decrease in absorption capacity, however, a big difference in performance between alloys. The PCT curve (absorption only) at 300 ° C clearly shows the improvement in hydrogen absorption from 5.7% by weight (unmodified) to 6.6% by weight (High Na, addition of Ca and Zr) or 6, 8% by weight (at the bottom).

[038] Figure 6 is a summary of the maximum hydrogen absorption capacity obtained from the results shown in figure 5. It can be seen that at 350 ° C, the maximum hydrogen storage capacity is similar (around 7% by weight) ) for all fused samples.

12/14 [039] At 250 ° C the modified alloys are superior and the maximum hydrogen capacity can be increased by more than 1% by weight compared to the unmodified alloy (from 5.3% by weight to 6.5% by weight).

[040] Even at 200 ° C (up to 2 MPa condition), the samples showed absorption of approximately 5.5% by weight of hydrogen.

[041] Regarding the desorption temperature, generally at a fixed pressure, the absorption temperature is lower than the desorption temperature. Exact temperatures will vary, depending on the pressure. Figure 7 shows the relationship between adsorption and desorption for an unmodified Mg 14Ni alloy at 0.2 MPa. The starting temperature of adsorption 1 is generally higher than the final temperature of adsorption 2. When the alloy then passes through the desorption cycle, the starting temperature of desorption 3 can be seen as higher than the final desorption temperature 4.

[042] In the representation of the modified alloys of Examples 2-6 in relation to the unmodified alloys, it can be seen that the final desorption temperature (plateau region in figure 8) at 0.2 MPa decreases approximately 20 ° C with the modification . In fact, the desorption temperature for the Mg Ni alloy can be reduced by adding trace elements.

[043] The addition of the modification elements increases the amount of internal interfacial areas of the material, the amount of stacking failures and the density of displacements / twinning in the solidified magnesium-nickel alloy. It is believed that the refinement element may have an atomic radius in the range mentioned above, so

13/14 to obtain the metallurgical effects on the metal as molten metal.

[044] The increase in displacements caused by additions is illustrated in SEM micrographs, figures 9 {a) ~ 9 (h). Figure 9 (a) is the SEM for Mg 14 Ni unmodified; figure 9 (b) is the SEM for the same alloy with addition of Zr; figure 9 (c) is the SEM for low sodium addition; Figure 9 (d) is SEM for high sodium addition; figure 9 (e) is the SEM for adding calcium; and figure 9 (f) is the SEM for adding Eu. Figure 9 (g) is the unmodified Mg 14 Ni alloy of greater magnification; figure 9 (h) is the low addition of sodium at the highest magnification of figure 9 (g).

[045] Figure 9 shows SEM electron images of hypoeutectic alloys Mg-14% by weight of unmodified (a) and! G) Ni; (b) 2 wt.% addition of Zr; (c) and (h) 600 ppm Na addition, (d) 2,400 ppm Na addition, (e) 800 ppm Ca addition and (f) Eu addition alloys at 600 ppm. The black part in the figures represents primary Mg dendrites and the small black part and the white contrast represent the Mg-Mg2Ni eutectic structure. The images clearly demonstrate a very refined fibrous eutectic microstructure in all modified samples compared to the coarse eutectic microstructure in the unmodified sample.

[046] All modified samples show a relative improvement of approximately 1% by weight to the maximum hydrogen absorption capacity. The refinement of the structure, even at levels of trace addition, is considered remarkable the yields of eutectic below 1 rim and frequently below 500 nm. Thus, a nano-scale material is obtained through the spacing

14/14 combination of an alloy modification and a fusion method

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Claims (10)

1. Method of production of a hydrogen storage material, characterized by the fact that it includes the steps of: formation of a hypoeutectic magnesium-nickel fusion, in which the magnesium-nickel fusion contains nickels within the range greater than zero up to 20%; adding up to 2% by weight of a refining element to the melt under a non-oxidizing atmosphere, the refining element having an atomic radius in the range of 1-1.65 times the atomic radius of magnesium; at least one element selected from the group consisting of Zr, Na, K, Ba, Ca, Sr, La, Y, Yb, Rb, Cs and Eu, where Zr is used only in combination with at least one other element of said group; and smelting smelting to produce the hydrogen storage material. 2. Method according to claim 1, characterized in that the magnesium-nickel fusion contains nickel within the range of 10-20% by weight. 3. Method according to claim 1, characterized in that the refinement element is added at an addition rate of up to 2,400 ppm. 4. Hypoeutectic magnesium-nickel alloy, characterized by the fact that it consists of: nickel in an amount greater than zero up to 20% by weight; more zero and up until 2% by weight of an element of refinement, the element in refinement having a radius atomic in range 1 The 1.65 times the atomic radius of the 2/3 magnesium; the refinement element being at least one element selected from the group consisting of Zr, Na, K, Ba, Ca, Sr, La, Y, Yb, Rb, Cs and Eu; where Zr is used only in combination with at least one other member of said group; and the rest of magnesium and incidental impurities. 5. Alloy according to claim 4, characterized by the fact that nickel is present in an amount of 10-20% by weight. 6. Magnesium-nickel alloy, according to claim 4, characterized by the fact that the refinement element is present in addition rates above zero and up to 2,400 ppm. 7. Magnesium-nickel alloy, according to claim 4, characterized by the fact that the alloy as a fusion has a refined eutectic structure with twinning in the magnesium-nickel intermetallic phase. 8. Hydrogen storage material formed from a fused magnesium-nickel alloy, the alloy being a hypoeutectic magnesium-nickel alloy, characterized by the fact that it includes: nickel in an amount greater than zero up to 20% by weight; more than zero and up to 2% by weight of a refinement element, the refinement element having an atomic radius in the range of 1 to 1.65 times the atomic radius of magnesium; the refinement element being at least one element selected from the group consisting of Zr, Na, K, Ba, 3/3 Ca, Sr, La, Y, Yb, Rb, Cs and Eu; where Zr is used only in combination with at least one other member of said group; and the rest being magnesium and incidental impurities. 9. Hydrogen storage material, according to claim 8, characterized by the fact that the alloy, as a fusion, has a refined eutectic structure with twinning in the magnesium-nickel intermetallic phase. 10. Material according to claim 8, characterized by the fact that the nickel content of the hypoeutectic magnesium-nickel alloy is 10-20% by weight. 1/16 Starting point (2MPa) 2/16 Samples Fig 2 3/16 Pressure (MPa) Hydrogen concentration, (% by weight) Fig3 4/16 PCT (300 ° C) 0.1 0.01 0.001 Pressure (MPa) - · ...... Mg MNi 300 ³ C absorption —A— + At high 300 ° C absorption ”—®— * Ca 300 ° G absorption —q_. + EU 3'00 ° C absorption ......... — .......... + Zr 300® C ab ortion - □ - + Nai> * bío300 ^o C jj lj I i 'iiii j ..... ..... iii »iii— ¹ ? I ii? I iii 0 1 2 3 4 5 6 Hydrogen concentration, (% by weight) Fig 4 5/16 PCT (250 ° C) Pressure (MPa) 0.01 Mg14Ni 250 ° C absorption - ± - + High 250¾ absorption -— + Ca 250 ° C absorption -O— + Eu 250 ° C absorption + ΖΓ 250 ^Φ C absorption -o— + Na beoeo250 ^o c budget 0.001 -i — i — u j — u -8 -L -........... I - J -I —ί ....... Hydrogen concentration, (¾ by weight) 6/16 Hydrogen absorption capacity (% by weight) 7.5 r— 7 I 6.5 * 6 · 5.5 J 5 ^: * 4.5; 150 200 250 300 350 Temperature (° C) JL — JL — and 400 Fig 6 7/16 Relative hydrogen value 8/16 1.2 Relative hydrogen value 0.8 0.6 0.4 0.2 Desorption at 0.2 MPa Mg 14 Ni ss ss ortion In «Ho Ca, » ₌ . _I ...... »- Zr (Ma low 280 290 300 310 320 330 Temperature ( ^c c) 340 350 Fig 8 9/16 Fig- 9 (a)